The "Flu" and Pregnancy: Get Smart, Get Vaccinated NOW

Well, the flu season is underway, and every pregnant woman wants to know, “Should I get the flu shot?” The simple answer is “YES (with few exceptions),” no matter how early or far along you are in your pregnancy, and the optimal time to receive the vaccine is now, during October and November (Obstet Gynecol. 2004;104:1125-6).

During an average flu season (October-May; peak December-March) in the U.S., 10-20% of individuals will contract the virus that causes the flu, 20-40,000 will die from it, and about 300,000 will be hospitalized due to complications. The flu is spread via the respiratory route by coughing, sneezing, and even speaking, and by self-inoculation from contact with surfaces that have been contaminated with respiratory tract fluids from an infected individual. Not every “cold” people get during the flu season is actually the result of infection with the influenza virus. There are MANY other “cold” viruses. Influenza usually causes a more severe illness than many of these and is often associated with high fever, headache, sore throat, cough (usually ‘dry’ and ‘nonproductive’), extreme fatigue, and muscle aches. Occasionally, people will have nausea, vomiting, and diarrhea as well, but these are not really typical of the flu, especially in adults.

Pregnant women are no more likely to contract the virus than other women, but they are more susceptible to developing more complicated infections, including influenza pneumonia, that may require hospitalization for respiratory compromise, high fever, and dehydration, as well as more serious complications associated with superimposed bacterial pneumonia. The latter was first recognized during the Great Flu (“Spanish flu”) Pandemic of 1918 that claimed 20-40,000,000 people worldwide. Indeed, it is now thought that many of these deaths were related to secondary infections with Staphylococcus aureus and not Streptococcus pneumonia, the more common cause of ‘milder’ bacterial pneumonia. This is a frightening prospect as this and future flu seasons loom because of the increasing prevalence of antibiotic-resistant Staphylococcus (MRSA) in the community (see my recent post “Postmortem Postscript: Staphylococcal Pneumonia”).

In 2004, the U.S. Advisory Committee on Immunization Practices (ACIP) recommended for the first time that all pregnant women annually receive the heat-inactivated (no live virus) trivalent influenza vaccine. This vaccine varies each year depending on the strains of the flu virus that are anticipated for the upcoming season. The influenza virus frequently ‘mutates’ so that even if you have had the flu before, you may not be immune to this year’s varieties. When the correct strains are chosen for vaccine production, it is estimated that both hospitalization and death among young, healthy recipients are reduced by 70-90%. It is not recommended that pregnant women take the live attenuated virus vaccine (LAIV).

It is especially important that you get the vaccine if you are pregnant and have medical conditions (diabetes, HIV, autoimmune disorders, organ transplant patients) that are accompanied by some degree of immunocompromise (by virtue of either the disease or the treatment), chronic lung disease (asthma, COPD, tobacco abuse), or anemia. Despite the recommendations, proven safety, and benefits of the flu vaccine, in recent studies generally less than 10% of pregnant women actually received the vaccine. The most common reason cited for this was “maternal concern” regarding vaccine safety for themselves and their babies (Naleway AL, et. al., Epidemiol Rev. 2006;28:47-53). However, this may also be the consequence of providers not doing their share in providing good information to their patients. A recent survey of OB/GYNs practicing in the U.S. revealed that only half would offer the flu vaccine to their pregnant patients in first trimester and more than one-third did not offer it at all in their practices (MMWR Morb Mortal Wkly Rep. 2005;54:1050-2).

The flu vaccine will not give you the flu. Some individuals will be sore at the site of injection (usually the deltoid muscle) and may even run a very low grade fever as their immune system mounts a response to the vaccine, but this is uncommon. Even if you have gotten the vaccine, and it was selected correctly for the strain of flu that season, you might still get the flu. However, symptoms are usually much milder and it is very unlikely that you will develop influenza pneumonia, require hospitalization, or die from the disease. A milder case of the flu probably reduces the risks to your baby as well. The vaccine also will not protect you from other viruses that can cause “colds” during flu season.

Contraindications to receiving the vaccine include allergies to chicken eggs (in which the vaccine is produced), thimerosal (preservative containing a small amount of mercury), and a history of allergic reaction to a flu vaccine in the past. You should also not get the vaccine in the rare event that you are the 1 in a million patient who suffered a condition called Giuillain-Barré Syndrome within 6 weeks of having previously received a flu vaccine. The vaccine during pregnancy is probably safer than waiting and relying on the use of drugs that might be used to treat an influenza infection once it is established.

The flu virus itself does not cross the placenta and infect the baby. However, maternal infection with the virus can be associated with fetal complications, particularly if contracted in the first trimester, as well as preterm labor and low birth-weight. Fetal anomalies are probably associated with maternal fever (hyperthermia), and perhaps inflammatory substances produced by the immune system in response to the organism, during the period of fetal organogenesis. The consequences of fever depend on the extent and duration of temperature elevation and the stage of fetal development when it occurs.

In experimental animals, hyperthermia has been shown to cause fetal abnormalities such as neural tube defects, small brains (micrencephaly), small eyes (microphthalmia), cataracts, facial clefts, skeletal, and heart abnormalities, among many others, as well as behavioral problems (Edwards MJ. Birth Defects Res A Clin Mol Teratol. 2006;76:507-16). Nearly all of these have been found in epidemiological studies following maternal fever during pregnancy. A recent study confirmed a higher prevalence of facial clefting, neural tube defects, and heart abnormalities among babies whose mothers had the flu during the 2nd and 3rd months of pregnancy (Acs N. Birth Defects Res A Clin Mol Teratol. 2006;73:989-96). There is some suggestion that the developing brain and nervous system might be sensitive to hyperthermia even beyond first trimester. Several studies have shown behavioral problems and, possibly, an increased risk for schizophrenia among offspring of women who have had the flu during pregnancy.

So, if you are pregnant, get the flu vaccine, encourage other family members to be vaccinated as well, avoid other people who may have the flu, wash your hands often when in ‘public places,’ and try not to touch your eyes, nose, and mouth when you have come in contact with surfaces that have a high risk of contamination! And, if you do get the flu, make sure you let your provider know, especially if you run a high fever, develop a ‘productive’ cough, or have any respiratory difficulties whatsoever….

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